Method for making jointed concrete structures

ABSTRACT

CONCRETE IS CAST WITH A DUMMY JOINT SEALED BY A FLEXIBLE WATER STOP EMBEDDED BY KEYING FORMATIONS INTO THE CONCRETE, BY A METHOD IN WHICH A CRACK IS FORMED AS THE DUMMY JOINT, A CRACK-INDUCING BODY, EG., A PIECE OF WOOD BEING FIXED IN POSITION, E.G., BY SPRING CLIPS, OPPOSITE THE CENTRE LINE OF EACH WATER STOP. THE INVENTION ALSO INCLUDES A NOVEL ASSEMBLY OF A WATER STOP AND A SPRING CLIP FOR HOLDING THE CRACK-INDUCING BODY.

May 11, 1971 J. HURST 3,578,733

METHOD FOR MAKING JOINTED CONCRETE STRUCTURES Filed May 23, 1968 2 Sheets-Sheet 1 METHOD FQH MAKING JOINTED CONCRETE STRUCTURES Filed May 23, 1968 J. HURST May 11, 1911 2 Sheets-Sheet 2 United States Patent 3,578,733 METHOD FOR MAKING JOINTED CONCRETE STRUCTURES John Hurst, London, England, assignor to W. R. Grace & Co., New York, N.Y. Filed May 23, 1968, Ser. No. 731,374 Claims priority, application Great Britain, May 26, 1967, 24,716/67 Int. Cl. E04b 1/16 US. Cl. 264-35 8 Claims ABSTRACT OF THE DISCLOSURE Concrete is cast with a dummy joint sealed by a flexible water stop embedded by keying formations into the concrete, by a method in which a crack is formed as the dummy joint, a crack-inducing body, e.g., a piece of wood being fixed in position, e.g., by spring clips, opposite the centre line of each water stop. The invention also includes a novel assembly of a water stop and a spring clip for holding the crack-inducing body.

This invention relates to concrete structures.

When concrete dries out after pouring, it contracts, and unless special measures are taken to prevent this, cracks tend to develop randomly in the concrete. Such cracks are highly disadvantageous in that they allow water to percolate through the concrete, and this problem becomes more serious with the passage of time, since the expansion and contraction of the concrete induces fresh cracks and enlarges those already present. It has long been the practice to mitigate the seriousness of this problem by intentionally introducing a plane of weakness into the concrete, as a result of which the cracks develop along the plane of weakness and not elsewhere. The plane of weakness is conventionally introduced by forming a depression in the surface of the concrete, for example by means of a V-shaped batten placed against the formwork or a saw cut made in the surface of the concrete. The crack is then sealed by the application of a sealing compound to the depression. A difiiculty that arises with such dummy joints, as these induced cracks are known, is that they can only be sealed by the application of a sealing compound and such sealing is not effective against any substantial pressure of water, particularly when the water pressure tends to displace the sealing compound, and furthermore the sealing markedly less effective with the passage of time. In addition, where reinforced concrete is used, the reinforcement is on the wet side of the sealing strip and is, therefore, liable to corrosion. Other methods of sealing dummy joints have been proposed but none is a practicable proposition. Thus the conventional method of sealing joints between separately poured masses of concrete, namely, by a strip of rubber or rubberlike material of dumb-bell crosssection, one half of which is embedded in each mass of concrete, is not applicable to dummy joints because it is impossible to place the water stop accurately in the middle of the poured concrete in relation to the subsequently induced crack. As a result, it has not hitherto been possible to use dummy joints in concrete structures below ground or in other places where a substantial water pressure is to be expected. Instead, since some form of joint is essential at regular intervals in a concrete structure, in order to ensure that expansion and contraction of the concrete is accommodated without the development of random cracking, it has been necessary to form expansion, contraction or construction joints; such joints, which are formed by adjacent and separately poured masses of concrete, can be effectively sealed, even against substantial water pressures, by means of water stops. However, the making of such joints is extremely time-consuming and 3,578,733 Patented May 11, 1971 expensive, since the first mass of concrete must be allowed to harden before the second mass can be poured and must of course be supported by formwork while it hardens. Where a long length of concrete is to be layed, it is usual to employ alternate bay construction, as illustrated in FIG. 2 of the accompanying drawings.

We have now surprisingly discovered that, contrary to the long established and accepted belief of those skilled in the art, it is possible, by, making use of a novel waterstop assembly, to form a dummy joint in a concrete structure so that the joint is effectively sealed by a water stop, even against substantial pressures of water, as in structures below ground. The method of the invention will be described chiefly by reference to joints running vertically through a generally horizontal structure, e.g., the base of a building; it is to be understood, however, that it is equally applicable to other dummy joints, e.g., in walls.

Our British specification Nos. 1,008,811 and 1,008,812 disclose a novel form of water stop which is described for use in the sealing of a concrete joint formed by two adjacent and separately poured masses of concrete, i.e., an expansion, contraction or construction joint; the said joint is sealed by a water stop in the form of an extruded or moulded section of rubber or other moisture and waterresistant flexible plastics material, the extruded or moulded section comprising a striplike body having at least one formation broadening out from its root for keying into concrete projecting laterally from the water stop on each side of the centre line thereof, the keying formations all projecting from the same face of the water stop and being so placed that outside each of the keying formations nearest the centre line of the water stop there is a portion of the water stop through which nails may be driven to secure the water stop to shuttering; the said water stop, which is referred to hereinafter as a water stop as hereinbefore defined, is positioned with the keying formations of the water stop embedded in the concrete whilst the outer face of the water stop is not embedded in concrete, so that the joint falls between the two keying formations nearest the centre line of the water stop.

A water stop as hereinbefore defined is illustrated, in perspective view, in FIG. 1 of the accompanying drawings.

The term keying formation broadening out from its root is used herein to include any formation which will key satisfactorily into concrete and is broader at some point more remote from the striplike body than it is at another point closer to the striplike body. For example the keying formation can be T-shaped or in the shape of an inverted truncated triangle. Generally, the keying formations will all be the same shape, but this is not necessary.

We have now discovered that by using a water stop as hereinbefore defined in a particular water stop assembly, it can be used to provide a water stop across a dummy joint. This discovery is of great importance because it makes possible the pouring of much longer lengths of concrete than has hitherto been possible.

The method of the present invention comprises positioning a water stop as hereinbefore defined flat on a surface against which concrete is to be cast such as on a base onto which concrete is to be cast, and/or securing the water stop to shuttering, positioning a crack-inducing body within the space where the concrete is to be cast and opposite the centre line of the water stop, and casting concrete in a single pour which extends across the water stop and crack-inducing body, so that the keying formations of the water stop become embedded in the concrete, while the opposite face of the water stop is not embedded, and a crack (which constitutes a dummy joint) is caused subsequently to form between the keying formations. Such a crack-inducing body can be a projection integral with the water stop, but it is much preferred to use a piece of Wood or any other rigid or sernirigid material which is secured in place fater the water stop has been positioned against the base or shuttering. In this way, a building contractor need only have available to him one type of water stop, which is, however, used differently depending on the type of joint to be made (i.e., a dummy joint in accordance with the present invention or an expansion, construction or contraction joint in accordance with the invention of British specifications Nos. 1,008,811 and 1,088,812 referred to above). It s particularly preferred to secure the crack-inducing body in place by means of clips of suitable material such as metal, e.g., spring clips, which are themselves secured to the water stop at intervals along its length. Such clips are conveniently secured to lugs projecting from the face of the water stop and formed integrally therewith; such clip-securing lugs preferably broaden out from their roots (particularly when spring clips are used) and thus serve also as formations for keying into the concrete; particularly, When the clip-securing lugs broaden out from their roots, it is preferred that there should be a further keying formation outboard of each of the clip-securing lugs, so as to eliminate any danger of the creation of a water-path in the region of the clips. It is in any case preferred that the water stop should have at least two pairs of keying formations in order to ensure that the water stop is fully secured to the concrete and to ensure an adequate water barrier. In addition to the clips securing the base of the cracki-nducing body to the water stop, the body can also be held in place in other ways, for example by clips or Wires attached to the crack-inducing body and to reinforcing bars and/or to bars specially provided for this purpose which may or may not become embedded in the concrete.

The crack-inducing body may be secured so that it touches the centre portion of the water stop or so that it is separated therefrom, e.g., by a distance of 2.5 to 10, preferably 5 to centimetres. Such separation is particularly desirable when the concrete contains reinforcement, which can then pass underneath the crack-inducing means, as well as, of course, over the top of it. It is not generally convenient for reinforcement to pass through the crack-inducing means, though this possibility is not excluded from the present invention.

In addition to the crack-inducing body placed within the concrete, it is possible also further to weaken the concrete in the same plane by conventional means, by forming a depression in the surface of the concrete opposite to the water stop. Such conventional means alone are not, however, sufficient to ensure that the induced crack will terminate within the water stop, as is of course essential. The additional use of such conventional means is particularly desirable where a water barrier is required against water or moisture on both sides of the crack or where the appearance of the opposite face is important, because the depression can be filled in any suitable way. Thus a sealing compound is used when a water barrier is required against water or moisture on both sides of the crack, e.g., on roads and underground culverts.

The method of the present invention has the outstanding advantage that it makes it possible to prepare in a single pouring a long length of concrete of the kind which previously required to be formed in more than one stage, i.e., a length in excess of 4.5 to 7.5 metres, e.g., by use of the expensive and time-consuming method of alternate bay construction described above. The use of the method of the invention for this purpose is shown in FIG. 2 of the accompanying drawings.

The size of the water stop to be employed and. of the crack-inducing body will be to some extent dependent on the dimensions of the concrete structure and the water pressure to which the structure is likely to be exposed, as also will the distance between adjacent dummy joints where more than one is required. The height of the crackinducing body should generally be t. to /3 the depth of the concrete and the distance between adjacent dummy joints 3 to 7.5 metres, preferably about 4.5 metres.

As with all water stops, it is essential to provide a complete continuous barrier to water over the whole surface of the joint which is exposed to water or moisture pressure. The precise nature of the water barrier need not be the same over the whole surface of the joint (though this is usually desirable). A particular advantage of the novel water stop assembly is that two or more water stops can readily be joined together, if desired, to form a complete network. Thus where the water stop has to change direction and runs in two planes inclined to each other, e.g., the horizontal and vertical planes, it is a simple matter to achieve this by means of a suitable preformed junction piece, which (by reason of the material of which the water stop is made) can readily be j-ointe'd in situ to the main strips to form a continuous waterproof run of water stop. Alternatively the water stop can simply be bent through the desired angle. Likewise where joints intersect, suitably shaped junction pieces (e.g., in the form of a T, X or Y) can readily be employed. While the crack-inducing means will in general be somewhat more complicated in such situations, in order to ensure formation of the dummy joint in the required position, this does not present any difiiculty. Another particular advantage of the novel water stop assembly is the ease with which the water stop can be secured in any desired position against shuttering (formwork) by driving nails (preferably double-headed nails) through the water stop outside at least the innermost pair of keying formations; the water stop preferably has a nailing flange outside any of the keying formations, through which flange the nails are driven.

In the accompanying drawings:

FIG. 1 is a perspective view of a short length of water stop as described and illustrated in British specifications 1,008,811 and 1,008,812;

FIGS. 2 and 3 are side views of concrete cast respectively by a known method and by the method of the invention; and PIlgIG. 4 is a perspective view of a spring clip as shown in The water stop of FIG. 1 has already been referred to above; its comprises a body portion 1, having keying formations 3 and 4 on each side of the centre line, and a marginal portion 5 through which nails may be driven. The precise cross sections of the keying formations may be varied from those shown.

FIG. 2 shows concrete being cast by alternate bay construction upon a base 2, which may be of concrete or compacted earth. Concrete has been cast in the bays 4, supported by temporary stop end shutters 6, which are held erect by support 8. The bay 10 has not yet been cast. Beneath the junction of each bay is a water stop 12 (as shown in FIG. 1) to prevent entry of ground water.

In FIG. 3, the concrete 4 has been cast continuously without use of stop end shutters (except as may be needed at the end of a days pour). A crack-inducing piece of wood 14 is fixed by spring clips 16 to the inner keying formations of each water stop 12. FIG. 4 shows a perspective view of a preferred form of the clip 16, which may be fabricated from a single strip of tempered metal,

preferably steel. Two or more clips, depending on the length of the water stop (i.e., the width of the concrete) are used for each water stop. A nail may be passed through the wood 14 and through the hole 20 shown in FIG. 4 at the top of the clip, to assist in retaining the wood in position.

As an illustration of the advantage of the method of the invention, the following figures are provided. A piece of concrete 4.5 metres wide by 4.5 metres high by 300 metres long could be laid in about 70 Working days by the prior method illustrated in FIG. 2, and in only about 40 working days by the method of the invention as on the nature of the concrete and other factors.)

I claim:

1. A method of providing a water-sealed dummy joint in cast concrete slabs, which comprises; positioning flat on a surface against which concrete is to be cast a water stop having a striplike body and at least one keying formation projecting along and from each side of its centre line within the space where concrete is to be cast; positioning a relatively thin crack inducing body within the space where concrete is to be cast and occupying about V2 to the depth of the space, spaced from and sub stantially perpendicular to the water stop and opposite its centre line and spaced from the opposite surfaces of the space where concrete is to be cast; securing the crack-inducing body by clips to lugs formed on the water stop and casting concrete in a single pour which extends across the water stop and the crack inducing body so that the keying formations become embedded in the concrete while the opposite face of the water stop is not embedded, and a crack (which constitutes a dummy joint) is caused subsequently to form between the keying formations.

2. A method according to claim 1, wherein the crackinducing body is a piece of elongated rigid or semirigid material.

3. A method to claim 1, wherein the lugs to which the clips are secured also serve to key the water stop to the concrete.

4. A method according to claim 1, wherein more than one joint is formed in a single piece of concrete 6 and the distance between adjacent dummy joints is 3 to 7.5 metres.

5. A method according to claim 1, wherein the bottom of the crack-inducing body is separated from the water stop by a distance of 2.5 to 10 cm.

6. A method according to claim 1, wherein the water stop is secured to the shuttering by nails passing through a flange at the edge of the waterstop.

7. A method according to claim 6, wherein the water stop runs in two planes inclined to each other and is nailed to the shuttering in one or both such planes.

8. A method according to claim 7, wherein the angle between the two planes is formed by a preformed junction piece.

References Cited UNITED STATES PATENTS 2,282,335 5/1942 -Methven 94-51X 2,319,049 5/1943 Fischer 94-18 2,444,372 6/1948 Robertson 94-18 3,183,627 5/1965 Rice 94-18X ROBERT F. WHITE, Primary Examiner G. A-UVILLE, Assistant Examiner US. Cl. X.R. 

